Vulcanization of rubber



Patented Sept. 10, 1940 UNITED STATES. PATENT OFFICE 2,214,460 VU'LCANIZATION F RUBBER Marion W. Harman, Nitro, W. Va., assignor to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware No Drawing Original application April 11, 1933, Serial No. 665,568. Divided and this applica tion October 16, 1937, Serial No. 169,474

Claims.

wherein R is nitrogen, carbon or sulfur, X is sulfur or nitrogen and Y is sulfur or the acidic hydrogen atom of a mercaptothiazole. When R is sulfur X preferably is nitrogen and when R is Y nitrogen X preferably is sulfur. R and X may or not be parts of a ring. I

As examples of the above class of compounds wherein R is carbon,'X is sulfur and Y is sulfur are the compounds dithio benzoic acid disulfide and dithio salicylic acid disulfide.

5 of the above class of compounds wherein R is nitrogen, X is sulfur and Y is sulfur are the compounds tetramethyl'thiuram disulfide, tetraethyl thiuram disulfide and tetramethyl thiuram polysulfide. As examples of the above class of com- 1 pounds wherein R is sulfur, X is nitrogen and Y is the acidic hydrogen atom of a mercaptothiazole are the compounds mercapto-benzo-thiazole, mercapto-tolyl-thiazole and mercapto-naphthathiazole. As examples of the above class of compounds wherein R is sulfur, X is nitrogen and Y is sulfur are diEbenzo-thiazyl] -disulfide and polysulfide. In mercapto-benzo-thiazole, mercaptotolyl-thiazole, mercapto-naphtha-thiazole, di- [benzo-thiazyll -disulfide and di [benzo-thiazyl] polysulfide R and X are part of a ring.

Examples of isocycli'c bases that are reactive with the organic compounds hereinbefore set forth, possessing the grouping methyl amine, l-mthyll-amino hexahydroben zene, cyclohexyl amine and dicyolohexyl amine. The compounds thus obtained are typical members of the new and preferred class ,of rubber As examples vulcanization accelerators and are included within the scope of the present invention.

The following are to be understood as illustrative embodiments of the invention and not limitative of the scope thereof.

EXAMPLE I Substantially equi-molecular proportions of cyclohexyl amine and mercapto-benzo-thiazole were dissolved in boiling alcohol.

After solution thereof was effected,- the resulting solution was cooled andthe cyclohexyl amine salt of mercaptobenzo-thiazole, which separated out, was filtered off and dried. The desired reaction product was obtained in high yield and in nature was a crystalline material melting'at substantially 151-155 C. The product thus obtained was incorporated in the usual manner in a typical rubber gum stock comprising i Parts Pale crepe rubber 100 Zinc oxide I 5 Sulfur 3 Stearic acid 1 Accelerator 0.2

The rubber stock thus compounded was vulcanized and the cured rubber product tested with the following results.

From thezdata set forth in Table I, it is readily apparent that the new and preferred class of acc'elerators, for example the reaction product of cyclohexyl amine and mercapto-benzo-thiazole', are markedly strong in their accelerating effect, as 0.25% of accelerator based on the rubber content gives substantially as high a state of cure as 1% of most of the commercial accelerators.

The reaction product of cyclohexyl amine and mercapto-benzo-thiazole described above was also employed in a typical rubber tread stock comprising Parts Smoked sheet rubber -I Carbon black 50 Zinc oxide 5 Sulfur 3 Stearic acid 3 Pine tar 2 Accelerator 1 The rubber stock thus compounded was Vulcanized and the cured rubber product tested with the results obtained as set forth in Table II.

The data set forth in Table II show that the new class of accelerators, for example the reaction product of cyclohexyl amine and mercapto-benzo-thiazole, are also markedly efficient in rubber tread stocks.

If desirable, the new andimproved class of accelerators may be employed in conjunction with basic organic nitrogen containing accelerators. Thus, on employing the reaction product of cyclo-hexyl amine and mercapto-benzothiazole in conjunction with diphenyl guanidine, said reaction product is activated thereby and its accelerating action increased. Other basic organic nitrogen accelerators, as for example triphenyl guanidine and di ortho tolyl guanidine, may be similarly employed.

EXAMPLE II The reaction product of substantially equimolecular proportions of dicyclohexyl amine and mercapto-benzo-thiazole was prepared in a manner analogous to that employed in the preparation of Example I. The product so obtained was a pale yellow solid melting at I'll-172 C. The reaction product of dicycloheXyl amine and mercapto-benzo-thiazole prepared as described above Was incorporated in a rubber stock comprising Parts Pale crepe rubber 100 Zinc oxide 5 Sulfur 3 Stearic acid 1 Accelerator 0.5

After vulcanizing, the cured rubber product was found to possess the following tensile and modulus characteristics.

Other methods of preparing the preferred class of accelerators may be employed than that hereinbefore set forth. Thus the reactants, for example cyclohexyl amine and mer'capto-benzothiazole, may be melted together in the absence of a solvent. Again they may be reacted in the presence of water with suitable agitation and grinding as shown in Example III.

EXAMPLE III Substantially one molecular proportion of a mixture of substantially 50% of cyclohexyl amine and 50% of dicy-clohexyl amine was reacted with substantially one molecular proportion of mercapto-benzo-thiazole by adding the above reactants to a suitable amount of water so as to form a paste and intimately mixing and grinding the mix by any convenient means, as for example by agitating in a ball mill. Some heat of reaction developed. It is preferred, however, to maintain the reaction temperature at substantially 40 to 45 C. in order to avoid loss of the amine during the reaction. After completion of the reaction, the resulting solid is preferably removed from the reaction mass, as for example by filtration, and dried. The dried crystalline product prepared as described, melted at substantially to C. The product prepared as described was. incorporated in a gum stock comprising Parts Pale .crepe rubber 100 Zinc oxide u 5 Sulfur 3 Stearic acid 1 Accelerator 0.5

The compounded rubber stock was then vulcanized and the cured rubber product found to possess the modulus and tensile characteristics given in Table IV.

EXAMPLE IV Substantially one molecular proportion of di- [benzo-thiazyll-disulfide and substantially two molecular proportions of cycl-ohexyl amine were allowed to react at room temperature. The heat of reaction caused a rise in temperature to substantially 60 0. Heating was continued for substantially one hour at substantially 60 C. The product thus formed was a hard grindable solid, which was incorporated in a rubber stock in the usual manner comprising Parts Pale crepe rubber 100 Zinc oxide 5 Sulfur 3 Stearic acid 1 Reaction product of dibenzo-thiazyl-disulfide and cyclohexyl amine 0.5

The compounded rubber stock on vulcanizing and testing gave the following results.

The compounded stock described above, wherein the reaction product of di [benzo-thiazylldisulfide and cyclohexylamine was employed as an accelerator, showed no set up of prevulcanization as determined by the Williams plastometer (described by Williams, Industrial and Engineering Chemistry for 1924 (vol. 16, page 362, see also Krall, ibid, vol. 16, page 922)) on heating for 120 minutes at 200 F.

EXAMPLE V Substantially one molecular pro-portion of tetramethyl thiuram disulfide and substantially two molecular proportions of cyclohexyl amine were allowed to react at room temperature. The heat of reaction caused a rise in temperature to substantially 50 C. After further heating at 60 C. to complete the reaction, the product Was allowed to cool. The resulting product, comprising a yellow solid, was incorporated in a typical gum stock and found to possess the accelerating properties typical of the preferred class of new accelerators.

From the data hereinbefore set forth, it is readily apparent that the preferred class of vulcanization accelerators comprise a group of compounds that are particularly strong in their accelerating action properties and that the vulcanized rubber in which they are employed retain-s its desirable properties on continued vulcanization; that is to say it does not readily over cure.

If it is desirable to further slow down the acceleration of the preferred class of accelerators, this may be accomplished by employing therewith certain retarding agents, as for example aniline acid phthalate and diphenyl guanidine phthalate.

Aniline acid phthalate has the structural formula. of

o 0 OHJnNO Parts Pale crepe rubber Zinc oxide 5 Sulfur 3 Stearic acid I 1 Reaction product of cyclohexyl amine and mercapto-benzo-thiazole 0.15 Diphenyl guanidine phthalate 0.30

The compounded stock set forth above showed no set up or prevulcanization, as determined by the Williams plastometer described above on heating for 240 minutes at 200 F.

A rubber tread stock was compounded comprising Parts Smoked sheet rubber 100 Carbon black 50 Zinc oxide 5 Sulfur 3 Stearic acid 3 Pine tar 2 Reaction product of cyclohexyl amine and mercapto-benzo-thiazole 0.5 Aniline acid phthalate 0.5

Plastometer tests carried out as above described showed no set up or prevulcam'zation on heating the compounded stock for minutes at 200 F.

The reaction product of mercapto-benzo-thiazole and a mixture of 50% of cyclohexyl amine and 50% of dicyclohexyl amine has also been employed in typical gum and tread stocks in. conjunction with aniline acid phthalate and diphenyl guanidine phthalte, and the rubber stock found on test to be free from scorching properties.

The present invention is limited solely by the following claims, wherein it is intended to claim the invention as broadly as possible.

This is a division of co-pending application Serial No. 665,568, filed April 11, 1933, now Patent 2,100,692.

What is claimed is:

1. The process of vulcanizing rubber which comprises incorporating into rubber sulfur and a vulcanization accelerator comprising the prodnot obtained by reacting at room temperature anintimate mixture consisting of a thiuram disulfide and an isocyclic saturated organic amine containing at least one hydrogen atom on the amino nitrogen atom in the ratio of two molecular proportions of amine to one of the thiurum disulfide and heating the mixture.

2. The process of vulcanizing rubber which comprises incorporating into rubber a vulcanization accelerator comprising the product obtained by reacting at room temperature an intimate mixture consisting of an alkyl thiuram disulfide and a cyclohexyl primary amine in the ratio of two molecular proportions of amine to one of the thiuram disulfide and heating the mixture.

3. The process of vulcanizing rubber which comprises incorporating into rubber sulfur and a vulcanization accelerator comprising the product obtained by reacting at room temperature an intimate mixture consisting of a tetra alkyl thiuram disulfide and a cyclohexyl primary amine in the ratio of two molecular proportions of amine to one of the thiuram disulfide and heating the mixture'.

4. The process of vulcanizing rubber which comprises incorporating into rubber a vulcanization accelerator comprising the product obtained by reacting at room temperature an intimate mixture consisting of a thiuram polysulfide and an isocyclic saturated organic amine containing at least one hydrogen atom on the amino nitrogen atom in the ratio of two molecular proportions of amine to one of the thiuram polysulfide and heating the mixture.

5. The process of vulcanizing rubber which comprises incorporating into rubber sulfur and a vulcanization accelerator comrpising the product' obtained by reacting at room temperature an intimate mixture consisting of tetramethyl thiuram disulfide and cyclohexylamine in the ratio of two molecular proportions of amine to one of the thiuram disulfide and heating the mixture.

6. The vulcanized rubber product produced by incorporating into rubber sulfur and a vulcanization accelerator comprising the product obtained by reacting at room temperature an intimate mixture consisting of a thiuram disulfide and an isocyclic saturated organic amine containing at least one hydrogen atom on the amino nitrogen atom in the ratio of two molecular proportions of amine to one of the thiuram disulfide and heating the mixture.

7. The vulcanized rubber product produced by incorporating into rubber a vulcanization accelerator comprising the product obtained by reacting at room temperature an intimate mixture consisting of an alkyl thiuram disulfide and a cyclohexyl primary amine in the ratio of two 1 molecular proportions of amine to one of the thiuram disulfide and heating the mixture.

8. The vulcanized rubber product produced by incorporating into rubber sulfur and a vulcanization accelerator comprising the product obtained qby reacting at room temperature an intimate mixture consisting of a tetra alkyl thiuram disulfide and a cyclohexyl primary amine in the ratio of two molecular proportions of amine to one of the thiuram disulfide and heating the mixture.

9. The vulcanized rubber product produced by incorporating into rubber a vulcanization accelerator comprising the product obtained by reactingvat room. temperature an intimate mixture consisting of a thiuram polysulfide and an isocyclic saurated organic amine containing at least one hydrogen atom on the amino nitrogen atom in the ratio of two molecular proportions of amine to one of the thiuram polysulfide and heating the mixture.

10. The vulcanized rubber product produced by incorporating into rubber sulfur and a vulcanization accelerator comprising the product obtained by reacting at room temperature an intimate mixture consisting of tetra-methyl thiuram disulfide and cyclohexylamine in the ratio of two molecular proportions of amine to one of the thiuram disulfide and heating the mixture.

MARION W. HARMAN. 

